The invention concerns a paper machine felt for utilization especially in the press area of a paper machine, with a woven base and a fibrous layer, or lap, that is needled onto the woven base, with the woven base being equipped with at least two layers and the free ends of the paper machine felt being equipped with complementing steps with steps surfaces that extend between at least two layers, and with the paper machine felt being provided with a connecting element that transfers tensile force in closed condition and via which the ends can be or are tied.
A typical paper machine felt is described, for example, in U.S. Pat. No. 4,564,985. The paper machine felt has a woven base, or ground fabric, onto which a lap is needled from the paper side, with the fibers interspersing the woven base. The woven base consists of two superimposed fabrics, with the fabric on the machine side having double layers.
Such paper machine felts can be produced as endless material. There is however also the possibility of producing a seamed paper machine felt, equipping it with a pintle wire seam (see also EP-A-0 108 733, U.S. Pat. No. 4,698,250). Such felts are easier to mount in the paper machine. Production of such a felt occurs by equipping the woven base, which is initially closed with the pintle wire, with a needled-on lap and that then the paper machine felt is opened up for assembly into the press area of a paper machine by pulling out the wire. Before this step, the needled-on lap is cut open parallel to the wire seam so that a flap is created above the wire seam. The cutting process can also occur through the formation of complementing steps with step surfaces that extend between at least two woven base layers (U.S. Pat. No. 4,698,250).
During assembly in the paper machine, the ends of the paper machine felt are first connected with each other by sliding the wire into loops provided for this purpose. The wire then represents the connecting element, via which the tensile force is transferred during operation. After connection through the wire, the fronts of the flap and that of the next lap are glued or needled together, with gluing possibly also occurring with a spray-on hot melt type adhesive (see EP-A-0 354 738).
Gluing only occurs for the purpose of fastening the flap and has no effects associated with transferring the tensile force.
A wire seam will always represent discontinuity. This applies particularly to paper machine felts of the kind described here with multi-layer woven bases. Discontinuity leads to paper marks and vibration at high operating speeds. Additionally, a wire seam""s stability is limited.
The invention is therefore based on the task of designing the seam on a paper machine felt of the kind described above in such a way that discontinuity in the seam area and therefore paper marks and vibration are largely avoided, and also that no stability problems arise.
This task is resolved with the invention by utilizing the adhesive as the connecting element that transfers the tensile force. The invention""s basic idea is therefore not to create a wire seam, but rather to transfer the tensile force that occurs during revolutions in the paper machine via a glued joint or seam.
Surprisingly, it was proven that such a glued joint can provide sufficient tensile strength if appropriate gluing surfaces are available. For this, an overlapping of the step surfaces of 5 to 15 cm in running direction is sufficient. The connecting seam formed in this manner, however, is not only more durable; it also prevents paper marks and vibration at high operating speeds since the invented connecting seam basically forms no discontinuity and is at best affected only slightly in its permeability and compressibility.
One embodiment of the invention provides for at least one, preferably both, of the step surfaces to be equipped with an adhesive layer, via which the ends can be connected through activation or are connected upon activation.
According to another feature of the invention, the fronts are equipped with an adhesive layer on at least one end of the paper machine felt.
The adhesive layer should not be continuous, but rather porous so that permeability in this area is not limited at all or only insignificantly. This can occur by spraying on the adhesive, by utilizing adhesive felt or employing a grid design. The adhesive layer should preferably consist of a hot melt type adhesive, like the one described in EP-A-0 354 738, for example. Alternatively, the adhesive layer can also be formed by adhesive fibers that are incorporated into the lap.
As with wire seams, the seam generally runs at a right angle to the running direction of the paper machine felt. There is also the possibility of allowing the connecting seam to extend diagonally to the running direction.